The invention pertains to a spray powder which is sprayed, such as by thermal spraying techniques, onto the surface of the substrate to form a hardfacing on the substrate surface, as well as a part having such hardfacing thereon. More specifically, the invention pertains to the aforementioned spray powder which has excellent abrasion-resistant properties and excellent corrosion-resistant properties, as well as a part with such hardfacing thereon thereby having excellent abrasion-resistant properties and excellent corrosion-resistant properties.
Heretofore, spray powders have been used to form hardfacing on the surface of a substrate, such as a part, so as to protect the substrate from abrasion and corrosion. For example, Kennametal Inc., of Latrobe, Pa. (assignee of the present application) has heretofore made and sold a tungsten carbide-cobalt-chromium spray powder which produces a layer on a substrate with abrasion resistance and corrosion resistance.
The patent literature contains a number of patents which concern hardfacing alloys. For example, U.S. Pat. No. 4,013,453, to Patel, concerns a tungsten carbide-nickel powder hardfacing alloy. The alloy starts with two basic components; namely, a WC-Ni mixture and a nickel alloy (2.5-20% Cr, 0.5-6% Si, 0.5-5% B, up to 10% Fe, and the balance Ni). In the final alloy, the average WC content is between 10 to 30%. U.S. Pat. No. 4,526,618, to Keshavan et al., concerns an abrasion-resistant spray coating comprising (1) 78 to 88 wt % tungsten carbide, and (2) an alloy with 6-18% boron, 0-6% Si, 0-20% Cr, 0-5% Fe and the balance nickel. U.S. Pat. No. 3,725,017, to Prasse et al., concerns a hardfacing comprising a boronhardened tungsten phase in a matrix of nickel-chromium or nickel-aluminum. The '017 patent discloses the use of powders of tungsten carbide, boron and at least one alloying element (one or more of Co, Ni, Cr and A1) to produce the boron-hardened tungsten phase. U.S. Pat. No. 4,996,114, to Darrow, concerns a coating process and the resultant coating. The process comprises two basic steps. For the first step, one applies a coating of a binder (Co or Ni) and carbide grit to the surface of the substrate. The second step comprises carbiding, nitriding or boriding the surface so as to harden the surface of the binder without affecting the carbides. U.S. Pat. No. 4,124,737, to Wolfa et al., concerns a high temperature wear resistant coating comprising a Co-based alloy containing 17-35% Cr, 5-20% Ta, 0-2% Y, 0.25% Si, 0-3.0% Mn, 0.5-3.5% C, 0-14% A1 and 0-50% of at least one metal oxide (such as alumina). U.S. Pat. No. 4,414,029, to Newman et al., concerns a welding rod filler of macrocrystalline WC along with niobium alone or in combination molybdenum for use as a hardfacing.
While earlier spray powders have provided some degree of abrasion resistance and corrosion resistance, there has been a need to provide a spray powder with excellent abrasion-resistant properties in combination with excellent corrosion-resistant properties. Typical parts which require surface layers with excellent abrasion-resistant and excellent corrosion-resistant properties include the wetted parts in a chemical processing slurry pump which experience wear. Other typical parts include downhole drilling parts which experience wear and are in contact with "sour gas," i e. hydrogen sulfide.
The patent literature contains patents which disclose hardfacing layers which are supposed to provide corrosion-resistant properties. For example, U.S. Pat. No. 4,064,608, to Jaeqer, concerns a ferrous roll with a hardfacing alloy that is supposed to be heat, corrosion and wear resistant. The alloy may be nickel-base, iron-base or cobalt-base and include 0.5-5% B, 0.5-6% Si, and up to 3% carbon along with carbide formers such as W, Cr and Mo. U.S. Pat. No. 4,822,415, to Dorfman et al., concerns an iron-based thermal spray powder. According to the '415 patent, the goal of the powder is to provide an alloy with corrosion resistance, frictional wear resistance and abrasive wear resistance. The composition comprises 0-40% Cr, 1-40% Mo, 1-15% Cu, 0.2-5% B, 0-5% Si, 0.01-2% C, and the balance impurities with at least 30% Fe. The spray alloy does not contain WC.
Even though earlier patents mention corrosion-resistant hardfacing alloys, there remains the need to provide a spray powder for application as a hardfacing which has excellent abrasion-resistant properties and excellent corrosion-resistant properties.